Effect Of Transition Metal Doping Research Articles

Ab initiostudy of the effects of transition metal doping ofMg2NiH4

Mg2NiH4 is a promising hydrogen storage material with fast (de)hydrogenation kinetics. Its hydrogen desorption enthalpy, however, is too large for practical applications. In this paper we study the effects of transition metal doping by first-principles density functional theory calculations. We show that the hydrogen desorption enthalpy can be reduced by ~0.1 eV/H2 if one in eight Ni atoms is replaced by Cu or Fe. Replacing Ni by Co atoms, however, increases the hydrogen desorption enthalpy. We study the thermodynamic stability of the dopants in the hydrogenated and dehydrogenated phases. Doping with Co or Cu leads to marginally stable compounds, whereas doping with Fe leads to an unstable compound. The optical response of Mg2NiH4 is also substantially affected by doping. The direct gap in Mg2NiH4 is ~1.7 eV. Doping with Co, Fe, or Cu leads to impurity bands that reduce the direct gap by up to 0.5 eV.

The effect of transition metal doping on thermal conductivity of YB66

Abstract The effect of transition metal doping in YB66 has been studied with respect to increase its thermal conductivity. Single crystals of YB66 doped with 4th, 5th and 6th group transition metals were grown by floating zone method. A detailed structure analysis suggested that an existing special B—B pair at the (1/4, 1/4, 1/4) site of YB66 could be attributed to a phonon scattering center that causes the amorphous-like low thermal conductivity. It was found that 5th and 6th group transition metals of V, Cr, Nb and Mo substitute the B—B pair. By contrast 4th group transition metals such as Ti and Zr were found to enter another (x, x, x) site with x ∼ 0.135. Thermal conductivity of both Nb-doped and undoped YB66 was measured in the range 4 K ≤ T ≤ 150 K. Nb doping increased thermal conductivity of YB66 with a factor of about 2.

Effect of transition metal doping and carbon doping on thermoelectric properties of YB 66 single crystals

We have been investigating the high-temperature thermoelectric properties of some novel rare earth borides with a structure containing B 12 icosahedra. Doping effects on the TE properties in such systems were investigated for the first time. A series of Nb-doped YB 66 and C-doped YB 66 single crystals were grown by the floating zone method. The Nb-doped compounds have approximate chemical formulas ranging from YNb 0.30B 66 to YNb 0.33B 66 while the C-doped compound has a formula of YB 66C 0.6. The effect of Nb-doping on the thermoelectric properties was not monotonic and appears to be complex. As a result of Nb-doping, the room temperature resistivity and the characteristic temperature T 0 were considerably reduced. At room temperature the power factor of the Nb-doped YB 66 sample with 89% site occupancy was three times greater than that of non-doped YB 66. However, in the important high-temperature region, the non-doped sample actually exhibited the highest power factor for T > 550 K . Furthermore, owing to a structural feature of YB 66, thermal conductivity actually increases with doping of transition metals. Taking into account all the thermoelectric properties, transition metal doping of YB 66 is therefore not suitable for our purposes. On the other hand, doping of carbon, which is assumed not to go into the same sites as the transition metals, yielded a lowering of the thermal conductivity. Furthermore, contrary to Nb-doping, carbon doping did not result in a reversal of the relative magnitude of resistivity at extremely high temperatures and therefore, an increase in the figure of merit of factor 2 was realized at 1000 K.

Effect of transition metal doping on photocatalytic activity of WO 3 for water splitting under laser illumination: role of 3d-orbitals

The effect of different transition metals (Fe, Co, Ni, Cu and Zn), at different concentrations, on the photocatalytic activity of WO 3 for splitting of water into hydrogen and oxygen was studied under UV laser irradiation. Moreover, we investigated the role of the configuration of 3d-orbitals of the doped transition metals in enhancing, or hindering, the production of hydrogen and oxygen.

Effect of transition metal doping on crystallization of cloverite

Gallophosphate molecular sieves containing Mn, Co and Zn have been hydrothermally synthesized at 170 °C, using starting gels with transition metals, and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), etc. Each starting gel yielded cloverite (CLO)-type phase, and its crystallinity depended on the kind of transition metal in the starting gel. The addition of a small amount of ZnO to the starting gel was observed to be useful for the preparation of Zn-doped cloverite (Zn-CLO) with good crystallinity, i.e. ZnO promoted crystal growth. The results of estimated unit cells and chemical analysis suggested that Mn 2+ and Zn 2+ ions were incorporated into the frameworks of Mn- and Zn-doped cloverites (Mn-CLo and Zn-CLO), respectively.